The Yeast GTPase Mtg2p Is Required for Mitochondrial Translation and Partially Suppresses an rRNA Methyltransferase Mutant,mrm2

Abstract

The assembly of ribosomes involves the coordinated processing and modification of rRNAs with the temporal association of ribosomal proteins. This process is regulated by assembly factors such as helicases, modifying enzymes, and GTPases. In contrast to the assembly of cytoplasmic ribosomes, there is a paucity of information concerning the role of assembly proteins in the biogenesis of mitochondrial ribosomes. In this study, we demonstrate that the Saccharomyces cerevisiae GTPase Mtg2p (Yhr168wp) is essential for mitochondrial ribosome function. Cells lacking MTG2 lose their mitochondrial DNA, giving rise to petite cells. In addition, cells expressing a temperature-sensitive mgt2-1 allele are defective in mitochondrial protein synthesis and contain lowered levels of mitochondrial ribosomal subunits. Significantly, elevated levels of Mtg2p partially suppress the thermosensitive loss of mitochondrial DNA in a 21S rRNA methyltransferase mutant, mrm2. We propose that Mtg2p is involved in mitochondrial ribosome biogenesis. Consistent with this role, we show that Mtg2p is peripherally localized to the mitochondrial inner membrane and associates with the 54S large ribosomal subunit in a salt-dependent manner.

Translation Initiation inSaccharomyces cerevisiaeMitochondria: Functional Interactions Among Mitochondrial Ribosomal Protein Rsm28p, Initiation Factor 2, Methionyl-tRNA-Formyltransferase and Novel Protein Rmd9p

“…While some Rmd9p-TAP sedimented into the gradient, there were no distinct peaks (our unpublished results). This result strongly indicated that Rmd9p-TAP is not a true ribosomal protein, but did not rule out a weaker ribosomal association that could be detectable at lower salt concentrations (Datta et al 2004). We therefore subjected solubilized mitochondria to gradient sedimentation under low-salt (100 mm NH 4 Cl) conditions (Figure 4).…”

Regulation of the stringent response is the essential function of the conserved bacterial G protein CgtA in Vibrio cholerae

“…This is probably a conserved function because in other organisms, such as V. harveyi, B. subtilis, C. crescentus, and E. coli, CgtA interacts with the 50S ribosomal subunit and has been shown to be involved in assembly or stability of the 50S subunit (17,23,27,28). Interestingly, a yeast mitochondrial CgtA homolog is essential for translation, likely through an involvement in ribosome biogenesis (29). In C. crescentus, a temperature-sensitive mutant was isolated with a defect in 50S ribosome assembly or stability, but this defect occurred at both the permissive and restrictive temperatures, indicating that this is not the essential function of CgtA (28).…”

The Putative GTPase Encoded by MTG3 Functions in a Novel Pathway for Regulating Assembly of the Small Subunit of Yeast Mitochondrial Ribosomes

“…1C). In keeping with the nomenclature adopted previously for naming genes coding for GTPases that function in expression of the mitochondrial translation system (11,12), we propose MTG3 (mitochondrial GTPase) as a name for this gene.…”

“…MTG1 codes for a member of the YIqF GTPase family that has been implicated in assembly of the mitochondrial large ribosomal subunit (11). Mutations in MTG2 have also been shown to abolish mitochondrial translation (12). The product of this gene is a member of the Obg GTPase family that binds to the large ribosomal subunit and is likely to function in its assembly.…”